A typical security system includes event detectors, keypads and alarms linked to a control panel by wire or radio frequency signals. The event detectors might include contacts positioned at doors and windows, motion detectors covering the open space of halls and rooms and fire detectors secured to ceilings. The contacts change their normally open or closed state in response to an entry or exit, motion detectors sense the activity of intruders and fire detectors respond to heat, temperature changes or smoke. When such predetermined events are detected, signals are sent to the control panel and the panel activates a sounder, strobe or other appropriate alarm. The control panel may also send messages to a central monitoring facility.
The keypads provide for inputs to the system and display system status. Alpha-numeric keys permit data entry, while light emitting diodes (LEDs) and liquid crystal displays (LCDs) present system outputs. The system is controlled from the keypad by entering an appropriate identification number, permitting access to system control. Desired system status, such as "armed" or "disarmed," can then be entered. Similarly, system status can be confirmed at the keypad, including the alarm state of one or more zones in the protected area.
The keypads usually are located inside the protected area, in locations convenient for controlling the system throughout the day. Typical locations include entrance points and bedrooms. Operation is facilitated under otherwise dark conditions by self-illumination of the keypad. When building lights are extinguished at night, for example, the operating features are illuminated by internal light sources which typically are on all the time.
Although existing illumination approaches are satisfactory in many installations, constant illumination of the keypad is inconvenient under certain conditions. Bedroom installations, for example, call for reduced illumination, or none at all. Battery operated devices pose similar issues based on the limited energy supply. High security areas sometimes require a blacked out keypad. Touch activated illumination solves part of the problem, but the keypad still must be found in the dark before it is illuminated by touching.